1 Field of the Invention
The invention concerns contoured disposable diapers, especially diapers having stretchable and elastically contractable leg cuffs and waist bands. The invention particularly involves the problem of attaining improved fit to the wearer at insignificantly increased cost of manufacture compared to diapers now on the market.
2. Description of the Related Art
Typically the body of a disposable diaper is substantially nonstretchable and has three major elements: a liquid permeable topsheet to be placed against the wearer's body, a liquid impermeable backsheet to form the face of the diaper, and an absorbent element interposed between the topsheet and backsheet. At the present time, those three elements are provided by three separate sheets, although it has been proposed to incorporate the absorbent and topsheet elements into a single sheet.
Most disposable diapers are contoured or formfitting and their leg cuffs and waistbands are elastically contractable as illustrated in U.S. Pat. No. 4,515,595 (Kievet et al.). Although the elastic waistbands of the Kievet et al. patent extend completely across both ends of the diaper, it is more common for the waist elastic to extend only part way across each end as in U.K. Pat. Application GB No. 2,156,656 (Pomplun et al.). In a contoured disposable diaper, the ends of the waist portions are flared out to form ears, and typically an adhesive-bearing fastening tab is attached to the back ears.
The fastening tabs of most contoured diapers are aligned with the substantially nonstretchable body of the diaper, as in the above-discussed patent and patent application. Forces applied by a user to pull the diaper snugly around the buttocks often result in tearing at the ears. In French Pat. Publication No. 2,583,620 (Courtray) which was laid open Dec. 25, 1986, the fastening tabs are aligned with an elastic waist band in order to make the diaper leakproof at the waist.
In the process of manufacturing disposable diapers, tension is typically maintained longitudinally, and elastic strips can be put into the leg cuffs in a stretched condition without difficulty, but the same is not true with waist strips which extend transversely where there is no tension. Accordingly, the waist of the diaper usually is made stretchable and elastically contractable by adhering to the backsheet a flat strip of heat-elasticizable material, i.e., a material which is heat-shrinkable and then can be stretched elastically to its original unshrunk dimensions. Then, after cutting out the diaper, the diaper is heated to shrink the heat-elasticizable material, thus shirring the waist band. When the heat-elasticizable material is a plastic film which also is heat-sealable, it can be adhered to the backsheet either adhesively or by being heat-sealed to the backsheet.
A preferred heat-elasticizable material for shirring the waist is disclosed in U.S. Pat. No. 4,552,795 (Hansen et al.). Before being shirred, it comprises a substantially flat inelastic web to which has been heat-bonded a plurality of parallel elastomeric strands that have been extended to at least about three times their relaxed length. The strand-bearing web can be coated with a layer of pressure-sensitive adhesive to adhere it to the backsheet.
Instead of the waist band being stretchable and elastically contractable, some disposable diapers employ stretchable fastening tapes as in U.S. Pat. No. 3,800,796 (Jacob). Although the diaper of the Jacob patent is not contoured, stretchable fastening tapes have been used on disposable diapers which are contoured.
U.S. Pat. No. 4,381,781 (Sciaraffa et al.) says that when there is an elastic waist strip, "the folding of the diaper waist end, which must take place after the continuous web is cut into individual diapers, is extremely difficult to accomplish. This is because the leg elastic will retract the individual diaper lengthwise if it is not held entirely flat while moving rapidly along the production line until packaging and the folding operation while simultaneously holding the diaper flat cannot be done readily" (col. 1, lines 35-47). The Sciaraffa et al. patent avoids an elastic waist strip, by cutting, as shown in FIG. 1, "openings 70 and 72 through the joined topsheet 2 and backsheet 4. The openings 70 and 72 intersect the waist edge 18 such that there is no diaper material between each of the openings 70 and 72 and the waist edge 18 . . . Elastic layer material such as layers 78 and 80 is respectively disposed in the openings 70 and 72 and affixed to either the topsheet 2 or backsheet 4, or both, so that the layers 78 and 80 become an integral part of the diaper as shown in FIG. 7" (col. 4. lines 7-19). The "elastic layers 78 and 80 may respectively be located entirely or partially within the ears 42 and 44 or entirely laterally inward of the ears 42 and 44" (col. 4, lines 41-44). "Due to the inelasticity of the topsheet 2 and backsheet 4, or both, most of the transverse tensile stress is applied to the elastic layer 80 causing it to stretch and provide a snug fit between the skin of the wearer and the waist areas 8 and 10" (col. 5. lines 5-10).
The Sciaraffa et al. patent says: "The attaching of the elastic material to the back sheet and/or top sheet of the diaper requires only cutting the sheets as they move in web form, cutting the elastic material, and pressing the elastic material against one of the sheets. These manufacturing steps are all readily accomplished in conjunction with the usual high speed diaper production lines" (col. 2, lines 32-38). No mention is made of the need to maintain good registration and probable difficulties in attempting to do so. It is believed that the diaper of the Sciaraffa et al. patent has not appeared on the market.